With technical advancements of digital video display apparatuses being tremendous such as starting from about 320×200 dots as a resolution for displaying alphanumeric characters and ending now to a density as high as 1920×1080 dots (pixels), these digital video display apparatuses are connected to personal computers in ordinary households. There also exist the digital video display apparatuses having resolutions such as 8192×4320 dots and 7680×4320 dots by standard. Historically, however, the information processing apparatuses do not perform displaying with such high resolutions from the beginning.
Especially, the personal computer performs displaying with 640×480 dots as a basic resolution when booted and properly increases the resolution with starting an OS (Operating System).
In televisions, the basic resolutions (640×480 dots, 720×480 dots, 1280×720 dots) are predetermined. There exist many cases in which any one of these resolutions is switched over to another in the midst of displaying the video.
On the occasion of changing the resolution, video display signals and clock signals are temporarily stopped on the side of the information processing apparatus, and the signals with an increased resolution are output again. When resuming the output of the signals, however, the output of the signals is resumed without notifying the video processing apparatus.
Thus, in the case of the system with the resolution being switched over midway, when the resolution is switched over, the video signals coming from the information processing apparatus get into an unstable state in many cases. In the DVI (Digital Visual Interface) standard and the HDMI (High Definition Multimedia Interface) standard, there exists no interface that explicitly notifies the video display apparatus that the video display signals are stopped. Information on insertion and removal is transferred to and received from the video processing apparatus by use of +5 V power signals, while information on mutual connection is transferred to and received from the information processing apparatus by use of HPD (Hot Plug Detect) signals. These pieces of information are not information about whether the video is being output or not. Accordingly, it is unfeasible to restrain unstable video signals from being displayed for a short period of time when the resolution is switched over and to display the video quickly after being switched over. Therefore, the video display apparatus stops outputting the video by monitoring at all times that the clock signals are stopped.
When the resolution is switched over, a determination that the clock signals are stopped in the video display apparatus gets into a malfunction, and the unstable video is displayed in some cases.
In this case, a user might think that the information processing apparatus or the video display apparatus gets into a fault. Moreover, the video display apparatus displays a meaningless screen, resulting in consumption of futile electric power. Further, the video display apparatus receives the unstable signals, which might lead to destruction of an element in some cases.
When the video display signals are output again from the information processing apparatus in a clock stopping state, the video display apparatus monitors the clock signals, and hence it takes a period of time till determining that the clocks are stabilized. Therefore, it takes the time till the video is again displayed on the video display apparatus.
The power is supplied to the video display apparatus from the information processing apparatus via the +5 V terminal based on the DVI standard and the HDMI standard, and a signal of the +5 V terminal is used as a signal for notifying the video display apparatus that the information processing apparatus is connected. It is also developed to switch over or notify the video display/non-display of the video display apparatus by controlling the power signal line and the like in place of monitoring the stop of the clocks.
This system, however, mainly aims at supplying the electric power, and therefore a stray capacitance is extremely large, and the signal cannot be used as the signal for quickly switching over the video display/non-display. Further, the cut-off of the power source implies, i.e., that the interface is inserted and removed, so that communications for reading video processing apparatus information (EDID: Extended Display Identification Data) and for performing an authentication process (HDCP: High-Definition Content Protection) occur in the information processing apparatus immediately after the +5 V power signal has restored. This takes a period of time, and hence the quick switchover to the stable video cannot be attained.
Moreover, in the latest Display Port standard, the information processing apparatus and the video display apparatus perform the communications with each other via two terminals named “CONFIG”, thus giving notification that the video output is started or stopped.
Many items of information are, however, transferred and received through these communications, and the communications are too complicated if used only for displaying the video very soon when canceling the display of an unspecified video and switching over the video and require a cost for achievement. Further, there is no extra signal pin in the DVI standard and the HDMI standard, and implementation thereof cannot be done.
The DVI terminal and the HDMI terminal, e.g., “DDC”, “DATA/DDC” and “CLOCK” are changed to “CONFIG”, in which case such problems are solved that the unspecified video is displayed and it takes the time till the video is displayed. There is, however, no compatibility with a combination of the information processing apparatus and the video display apparatus according to the DVI standard and the HDMI standard.
[Patent document 1]    Japanese Laid-Open Patent Publication No. 2007-288407
[Patent document 2]    Japanese Laid-Open Patent Publication No. 2004-272132
[Patent document 3]    Japanese Laid-Open Patent Publication No. 2003-209920